1. Technical Field
The present invention is related to a color regulating device for illumination, a color regulating apparatus for illumination using the color regulating device, and a color regulating method.
2. Description of Related Art
Human life style has greatly changed since Edison invented incandescent lamps, and more durable, aesthetic and efficient illumination products have been advanced and developed continuously.
However, because sunlight has been adapted during the human evolution, human visual organs still favors natural illumination environment even when situated under artificial illumination. Sense of structures of human eyes to visible light changes based on variation of light wavelength and brightness of the environment. When visible light affects on human eyes to generate light sense, it is not only related to the composition and intensity of light, but also related to physiological characteristics of human visual organs and psychological factors of human. Therefore, it is necessary to evaluate visual effect generated by light radiation according to physiological characteristics of human eyes and agreed regulations through “light measurement.”
Because light measurement relies on physiological characteristics of human visual organs, the Commission Internationale de l'Eclariage (CIE) unifies and sets the evaluation standard of the light sensing capability of human eye. Human eye sensitivity function V(λ) has been set forth to connect and convert the radiation measurement and light measurement, and chromaticity diagrams are used to standardize to human eye sense of color. In 1924, CIE set forth that in an equal energy spectrum experiment of a small field of view of 2 degree, eye sensitivity function of a point light source under a photopic vision condition is called CIE 1931 eye sensitivity function and is relied to derive a CIE 1931 color space chromaticity diagram, as shown in FIG. 1. Because human eye has different light vision performance under different wavelengths, CIE, according to the human eye sensitivity to blue and indigo spectrum zones, sets forth CIE 1978 eye sensitivity function in 1978. This corrected function has higher responded value in the spectrum zone with wavelength being lower than 460 nm. However, although the CIE 1978 eye sensitivity function is the most accurate sensitivity description, the CIE 1391 is the most used color space chromaticity diagram in the world at present.
White light is the most widely used light source in the application of illumination. Because of the characteristics of the light metamerism, many spectrum combinations can be found from the chromaticity diagram to form white light. Because the characteristic difference amount all white lights is “color temperature,” the color temperature relative to the chromaticity coordinate becomes an importance parameter of describing the characteristic of white light source. “Color temperature” is the parameter of “absolute temperature of the surface of a black body” to represent a spectrum distribution of a light source when such spectrum distribution is the same of a spectrum radiated from the black body. (The black body means an object that absorbs the radiation of any wavelength falling downward to its surface at any temperature.) In summary, color temperature is an expressing manner defined according to light color variation emitted from black body radiation, and the expressing manner of the defined color employs the unit of absolute temperature Kelvin (K). When the black body is heated, the outer surface of the black body under different temperatures emits different colored light. For example, when heated to 1000K, the black body presents red, red-yellow is presented below 3000K, white is presented from about 3000K to 6500K, and white light turns a little blue over 6500K. Because “color temperature” can be simply used to describe a specific spectrum, it is used to be a standard in the illumination field.
According to temperature variation, the color temperature of the light emitted from the black body can be used to depict a locus in the chromaticity diagram. The locus of the black body radiation spectrum in the CIE 1931 color space chromaticity diagram is called “Planckian Locus” or Black Body Locus (BBL). The white light spectrum in the natural world is greatly similar to the Planckian spectrum. The locus aa′ in FIG. 1 indicates the “black body locus” of the Planckian black body radiation spectrum in the CIE 1931 color space chromaticity diagram and the corresponding color of its color temperature.
In the aspect of color temperature control, for a white light illuminating lamp, different color temperatures have different application fields. For example, the color temperature below 3,300 K is called “warm light,” which is close to the incandescent lamp, has more red composition and provides people with feelings of warmth, health and comfort. Therefore, warn color light is adapted suitably to families, residences, dormitories, guest houses or places with low temperatures, etc. The color temperature from 3,300 K to 5,300 K is called “cold white light.” Because such light is soft, it makes people feel joyful, comfortable and peaceful. Such cold light is adapted suitably to stores, hospitals, offices, restaurants and waiting rooms, etc. Color temperature over the absolute temperature 5,300 K is called “cold light,” which is most close to natural light, and is bright to make people concentrate. Such cold light is adapted suitably to offices, conference rooms, classrooms, drafting rooms, design rooms, reading rooms of libraries and display cabinets, etc. Therefore, a good white light illuminating device necessarily completes adjustment of color temperature to greatly increase its application and value.
Furthermore, to evaluate whether the white light source is close to natural light, “color rendering index” of an object under illumination also becomes an important parameter. The object under illumination of sunlight or an incandescent lamp shows so-called “true color” because the characteristics of broadband of such light sources. The level of the true color presented from the object by the light source is called “color rendering index (CRI or Ra)” to evaluate the color rendering of the light source. A standard light source is used as a reference value, and Ra thereof is 100; the rest of the light sources have Ra lower than 100. When Ra value is larger, the color rendering of the light source is better. The Ra of the incandescent lamp can reach to 98. Because human eyes evolve to adapt to daylight environment, CIE employs the black body radiation spectrum of Planckian locus as an evaluation basis. To daylight of every time phase falling into an extent at a little distance to the Planckian locus, the color rendering ratio is very high.
In the modern illumination apparatuses, the most common light sources include halogen lamps, fluorescent lamp, cold cathode fluorescent lamp (CCFL), and light emitting diodes (LEDs), etc. Once an illuminating light source is completely manufactured, both color temperature and color rendering thereof are not adjusted easily anymore. With regard to conventional illumination apparatuses, common incandescent tungsten lamps have good color rendering but short lifespan and low luminous efficiency. Halogen lamps have improved lifespan and luminous efficiency when compared with incandescent lamps but high heat and ultraviolet thereof are criticized. Furthermore, conventional illumination devices based on principles of operation of incandescent lamps are all limited by overheating and unchangeableness of color temperature and color rendering after leaving factories. With regard to CCFL, it is not eco-friendly because of contained mercury and also has problems of insufficient color rendering. Recently, LED comparatively has advantages of compact volume, excellent light emitting efficiency, long lifespan and quick operating reaction time and complies environmental protection requirements of non-radiation and non-poisonous material such mercury so that having superiority when compared with other conventional illuminating light sources.
An LED is fabricated by using semiconductor process technologies to realize an optical element based on semiconductor diodes, it converts electricity to light wave, radiation spectrum belongs to mono color light and wavelength includes infrared, visible light and ultraviolet. Because the LED is required to form illuminative white light, the wavelength spectrum needs to cross red, green and blue wavelength bands of three primary colors of light to further mix into light beam. In other words, the wavelength needs to cross 300 nm (from about 400 nm to 700 nm). However, because the energy difference of a full-width at half-maximum of the radiation spectrum of the LED is very narrow, it can only emit mono light with a mono wavelength. Since a long time ago, LED is limited by the slow development of blue light wavelength band of three primary colors, because the brightness of the emitted blue light was not good and thus it cannot achieve true color images and white light illumination.
To realize white light illumination of LED, methods used by businesses are classified into two types. The first method is to combine LED chips that emit different wavelengths. For example, combination of red, green and blue LEDs or combination of blue and yellow-green LEDs is used. Electric current regulating each LED is controlled separately and a light diffusing film layer is then applied to emitted LEDs to mix and form white light. The other method is to employ material capable of converting wavelength, such as a semiconductor, phosphor or dye to cooperate with a mono light LED to achieve the purpose of emitting white light. The matured one of such white light emitting technologies is the technology that uses phosphor to cooperate with mono light LED. In 1996, Nichia Chemical Industries, Ltd. of Japan developed to use blue (GaxIn1-xN) LED to cooperate with yttrium aluminum garnet (YAG) phosphor emitting out yellow light to form a white light source. Yellow phosphor absorbs part of blue light emitted by the blue LED and then radiates out yellow light with longer wavelength. Finally, the lights of different colors are mixed into white light. Such method only needs one group of LED chips of the same color. Another common phosphor is terbium aluminum garnet (TAG) phosphor, which has worse light emitting efficiency but exhibits better color rendering when compared with YAG. The present method, cooperating the wavelength converting material capable of converting wavelength of the mono color LED to achieve white light illumination, still cooperates blue LED with yellow YAG or TAG phosphor.
However, newly risen LED light sources still cannot replace conventional illumination apparatuses. The major cause is that all marketable LED lamp products lack the characteristic presenting a uniform color temperature so that difference of color temperature between products is inevitable. The marketable white light LEDs mostly use blue LEDs and yellow phosphor to mix color. The present blue light LED manufacturing process has gradually become mature. However, when the blue light LED cooperates with the yellow fluorescent light to mix and form white light, a bias away from a predetermined zone of color temperature happens due to the mixing of luminous flux generated from the blue light and yellow phosphor has great uncertainty so that the factory color temperature of each product cannot be controlled accurately. The causes of uncertainty include phosphor mixing ratio during manufacture, uniformity of phosphor distribution, time control of phosphor dispensing during mass production and corresponding LEDs which may have different characteristics. The present mass production of white light source by cooperating phosphor with LEDs still causes an inaccuracy of more than positive and negative 200K. However, human eyes can sense and feel the color temperature variation of a light source once the color temperature variation is more than positive and negative 100K. A more sensitive person can even become aware of color temperature difference down to 50K. Therefore, general illumination products have a tolerance reduced from 100K to 50K at present. White light LEDs are limited by many above-mentioned factors of uncertainty and the yield thereof is greatly decreased. Defective samples have no choice but sell by lowered prices.
FIG. 2 is a diagram of CIE 1931 chromaticity coordinate and color tolerance, which sets up specifications for the chromaticity of solid state lighting products for electric lamps of ANSI C78.377A of white light LEDs under different color temperatures. The intervening curve shown in FIG. 2 is part of the curvature aa′, a black body locus (BBL) in FIG. 1. The edge of each small grid along the up and down direction of BBL in FIG. 2 is about 50K, which represents that chromaticity within the grid is deemed “the same color temperature” because human eyes cannot distinguish any difference from color temperatures within the same grid. A common white light source for illumination has its color temperature at least inside a certain zone of the figure. Therefore, for a present indoor light source assembled from multiple LED chips, once any of the LED chips is damaged, all of the LED chips will need to be replaced completely to achieve the uniformity of color temperatures of all light sources.
As mentioned above, most of marketable white light LEDs use blue light LED and yellow phosphor to mix colors and the disadvantage thereof is that the factory color temperature of each product cannot be controlled. The reason for failure in accurate control is that the mixing of luminous flux of from the blue light and yellow phosphor has great uncertainty. Furthermore, a specific color temperature of each batch of white light sources is completed by mixing out a specific ratio of phosphor and the ratio cannot be changed by itself after package. Such method cannot arbitrarily adjust and change color temperature of the white light source so the applicability and value of the illumination apparatuses are greatly lowered. Moreover, the light source for indoor illumination should meet the criteria of suitable brightness, cozy light field, and color consistency between space and time. However, many LED light sources in the market have the issue of the space color shift, which refers to a “yellow halo” resulting from a blue shift in the middle and yellow shift in periphery. The space color shift may render adverse effect to the human body in the case of extremely high color temperature at certain angles.
In addition, at present three colors of red, blue and green LED light source are also used. With controlling the relative intensity by circuit, a white LED light can be made. However, in that three colors have different decay rates (in which red LED is the fast one), a significant color shift occurs after using for a period of time. The present various light sources for illumination apparatuses or adjustment of wavelength, including LEDs, have serious problems on or cannot completely control the variation and adjustment of color temperature and color rendering. To increase the quality of light sources and the application value of products (for example, illumination), the present light source devices such as for illumination have great difficulty to overcome. Therefore, a method how to accurately adjust the spectrum distribution or wavelength band of final outgoing light is greatly valuable in applications of illumination and may be used in the other application fields that highly require the quality of light sources.